Problem: Solve for $q$ : $q - 7 = -20$
Answer: Add $7$ to both sides: $ \begin{eqnarray} \\ q - 7 &=& -20 \\ \\ {+7} && {+7} \end{eqnarray} $ $ \begin{eqnarray} \hphantom{-7 + q} &\hphantom{=}& \hphantom{-20} \\ q &=& -20 {+ 7} \\ \end{eqnarray} $ Simplify. $ q = -13$